1. Field of the Invention
This invention is concerned with means for imparting improved adhesion to polyolefin substrates, especially polypropylene, of acrylic-based or other protective polymers, in the form of a plastic coating or a latex or solvent-based paint. The invention may be further applied to improve adherence or adhesion of pressure sensitive adhesives, which adhesives may serve to bond cloth, carpet, non-woven fabrics, plastics, and the like to the improved substrate. The invention is further concerned with means to an improved substrate for adherence of inks and colorants.
2. Description of the Prior Art
Matrix polyolefins used as substrates for acrylic plastics or for paints, inks, or latices, where the latter impart weatherability, decorative effects, printability, and the like, are useful in the assemblage of automobiles and other vehicles, such as automotive interiors, trunks (boots), truck (lorry) cabs, automotive exteriors, such as fender liners, bumpers, and the like, railroad car interiors, van (caravan) trim, and the like, equipment housing, furniture, and the like, where they offer advantages in cost and formability over metal or wood. Unfortunately, the polyolefins such as polypropylene or polyethylene do not adhere well without special treatment.
It was earlier found (U.S. patent application No. 93,126, filed Jul. 16, 1993) that acrylic plastics, more specifically polymers of methyl methacrylate, are useful for the above purposes when combined with a cheaper, tougher polyolefin in a laminar structure (which structure may require a laminating adhesive in the case of polyolefins to prevent delamination), and disclosed many potential uses for such a combination. In U.S. Pat. No. 4,957,974 is disclosed the use of specific graft copolymers of polyolefins and polymethacrylates, when further blended with polypropylene, as useful for improving printability, and the graft copolymers as tie layers between otherwise incompatible polymers. In U.S. Pat. No. 5,035,933 is disclosed the use of such graft copolymers as tie layers between polyolefins and certain barrier polymers. In U.S. Pat. No. 5,237,004 is disclosed a thermoplastic composition having modified optical properties which comprises a thermoplastic matrix polymer and distributed throughout the matrix polymer from about 0.1% to about 40% of the total composition weight of spherical particles of core/shell having an average diameter of from about 2 to about 15 microns (and a narrow particle size distribution), the outer shell of which is compatible with the matrix polymer. Polyolefins are known to the art to be incompatible with poly(methyl methacrylate). None of the above references teach or suggest the improved method for imparting adhesion to polyolefins disclosed herein.